In organic synthesis, a metathesis reaction is a catalytic reaction in which recombination of the double bonds occurs between two kinds of olefins or alkynes. The diversity of possible applications has led to the use of metathesis, particularly olefin metathesis, as a standard synthetic tool. Olefin metathesis applications include cross-metathesis (CM), ring-opening metathesis polymerization (ROMP), ring-opening cross metathesis (ROCM), ring-closing metathesis (RCM), and acyclic diene metathesis (ADMET). CM involves a carbon-carbon bond breaking/bond making process in which there is an overall exchange of double bond moieties between two olefins. ROMP involves the formation of polyolefins from the ring opening of cyclic olefins; ROCM involves a tandem sequence in which a cyclic olefin is opened and a second acyclic olefin is then cross metathesized onto the newly formed olefin termini; RCM involves the intramolecular transformation of an alpha, omega-diene to a cyclic olefin; and ADMET involves the polymerization of terminal dienes to polyenes. These synthetic tools have been applied to solve a wide range of synthetic problems, for example, RCM has been often featured as a key step in many synthetic solutions ranging from the total synthesis of natural products to the synthesis of catenanes. Also, industrially important polymers produced from ROMP include trans-polyoctenamer (polymer of cyclooctene, commercially available as Vestenamer® from Evonik Industries), polynorbornene (commercially available as Norsorex®); and polydicyclopentadiene (commercially available as Telene®, Metton®, and Pentam®). Another commercially significant application is ethenolysis, which is the CM of ethylene and internal olefins to produce alpha-olefins. Metathesis reactions are therefore indispensable as a synthetic tool for the formation of new carbon-carbon bonds.
Olefin metathesis may be catalyzed by one or more catalytic metals, usually one or more transition metals, such as the molybdenum-containing Schrock catalyst and the ruthenium- or osmium-containing Grubbs catalysts. Well-defined single component ruthenium or osmium catalysts have been previously described by, for example, U.S. Pat. Nos. 5,312,940; 5,342,909; 5,728,917; 5,710,298; 5,750,815; 5,831,108; 7,329,758; and PCT Publications WO 97/20865 and WO 97/29135, which are all incorporated herein by reference. These catalysts possess several advantageous properties, such as tolerance to a variety of functional groups and higher activity than previously known metathesis catalysts.
The ethenolysis of an internal olefin to produce linear alpha-olefins (LAOS) is of particular commercial significance. LAOs are useful as monomers or comonomers to produce polyalphaolefins (PAOs) and/or as intermediates in the production of epoxides, amines, oxo alcohols, synthetic lubricants, synthetic fatty acids, and alkylated aromatics. LAOs of industrial importance include 1-butene, 1-hexene, 1-octene, 1-decene, 1-undecene, 1-dodecene, and 1-tetradecene. However, the production of LAOs is often undesirably inefficient, creates unwanted by-products and wastes reactants and energy. Also, the major source of the starting materials for these commercial routes to LAOs are nonrenewable feedstreams including petroleum, coal, and natural gas.
Recently there has been a strong incentive to produce fuels and chemical products from renewable feedstreams, such as natural oils. For example, the development of biodiesel fuels is of great interest and some biodiesel-based materials are already commercially produced. Specifically, bio-diesel fuels made from plant oils are already on the market and demand for such fuels is expected to increase significantly over the next decade. LAOs may be produced from such renewable feedstreams by a CM reaction of the renewable feedstream, such as methyl oleate, with an olefin, such as ethylene, in the presence of a metathesis catalyst.
CM catalysts, reported thus far, for the ethenolysis of methyl oleate are typically ruthenium-based catalysts bearing phosphine or carbene ligands, such as those reported in Organometallics 2004, Vol. 23, No. 9, pp. 2027-2047 and WO 2008/010961. However, these catalysts were reported to be too expensive for industrial consideration due to high costs associated with the catalysts being derived from a low yielding synthesis (See Final Technical Report entitled “Platform Chemicals from an Oilseed Biorefinery,” grant number DE-FG36-04GO14016, awarded by the Department of Energy). Furthermore, these ruthenium alkylidene catalysts are usually prepared by the reaction of ruthenium species with diazo compounds (J. Am. Chem. Soc. 1999, Vol. 121, No. 4, pp. 791-799). Therefore, cost and safety concerns associated with industrial scale reactions comprising diazo compounds have led to increased efforts to prepare ruthenium alkylidenes via alternate synthetic routes, such as using propargyl and vinyl chlorides (Organometallics, 1997, Vol. 16, No. 18, pp. 3867-3869). In order to obtain a commercially viable metathesis-based process, for example, LAO production via the CM of ethylene and biodiesel or natural oils, higher activity metathesis catalysts must be discovered.
There remains a need for catalysts which demonstrate high activity and selectivity in metathesis transformations which are capable of being synthesized by mild, affordable, and simple synthetic routes. The new catalysts disclosed herein are useful for metathesis transformations such as ROMP, CM, ROCM, and other metathesis transformations. The inventors have surprisingly found that a metathesis catalyst composition comprising a Group 8 metal hydride-dihydrogen complex and a ligand exchange agent and, optionally, an acetylene generates an active metathesis catalyst. The metathesis catalyst compositions of the present invention provide mild, affordable, and simple synthetic routes to desirable olefins and polyolefins, for example, LAOS, which in turn may be useful in the preparation of PAOs; poly(cyclic olefins); and other industrially relevant chemicals.